Organic electroluminescent element

ABSTRACT

Provided is an organic electroluminescent device (organic EL device) which has improved luminous efficiency and a simple configuration, while ensuring sufficient driving stability. This organic electroluminescent device includes a light-emitting layer between an anode and a cathode that are laminated on a substrate. The light-emitting layer contains a phosphorescent light-emitting dopant, and a carbazole compound represented by the following formula (1) as a host material. In the formula (1), E represents oxygen or sulfur, and R 1  to R 6  each represent hydrogen, an alkyl group, a cycloalkyl group, or an aromatic group represented by the formula (2). In the formula (2), X represents CR 9  or nitrogen.

TECHNICAL FIELD

The present invention relates to an organic electroluminescent deviceusing a novel material for an organic electroluminescent device, andspecifically, to a thin-film-type device that emits light when anelectric field is applied to a light-emitting layer formed of an organiccompound.

BACKGROUND ART

In general, an organic electroluminescent device (hereinafter referredto as organic EL device) is constructed of a light-emitting layer and apair of counter electrodes interposing the light-emitting layertherebetween in its simplest structure. That is, the organic EL deviceuses the phenomenon that, when an electric field is applied between boththe electrodes, electrons are injected from a cathode and holes areinjected from an anode, and each electron and each hole recombine in thelight-emitting layer to emit light.

In recent years, progress has been made in developing an organic ELdevice using an organic thin film. In order to enhance luminousefficiency particularly, optimization of kinds of electrodes has beenattempted for the purpose of improving efficiency of injection ofcarriers from the electrodes. As a result, there has been developed adevice in which a hole-transporting layer formed of an aromatic diamineand a light-emitting layer formed of an 8-hydroxyquinoline aluminumcomplex (hereinafter referred to as Alq3) are formed between electrodesas thin films, resulting in a significant improvement in luminousefficiency, as compared to conventional devices in which a singlecrystal of anthracene molecules or the like is used. Thus, developmentof the above-mentioned organic EL device has been promoted in order toaccomplish its practical application to a high-performance flat panelhaving features such as self-luminescence and rapid response.

Further, studies have been made on using phosphorescent light ratherthan fluorescent light as an attempt to raise luminous efficiency of adevice. Many kinds of devices including the above-mentioned device inwhich a hole-transporting layer formed of an aromatic diamine and alight-emitting layer formed of Alq3 are formed emit light by usingfluorescent light emission. However, by using phosphorescent lightemission, that is, by using light emission from a triplet excited state,luminous efficiency is expected to be improved by about three times tofour times, as compared to the case of using conventional devices inwhich fluorescent light (singlet) is used. In order to accomplish thispurpose, studies have been made on adopting a coumarin derivative or abenzophenone derivative as a light-emitting layer, but extremely lowluminance has only been provided. Further, studies have been made onusing a europium complex as an attempt to use a triplet state, buthighly efficient light emission has not been accomplished. In recentyears, many studies centered on an organic metal complex such as aniridium complex have been made, as disclosed in Patent Literature 1, forthe purpose of attaining high luminous efficiency and a long lifetime.

CITATION LIST Patent Literature

-   [PTL 1] JP 2003-515897 A-   [PTL 2] JP 2001-313178 A-   [PTL 3] WO 2009/008100-   [PTL 4] JP 2011-509247 A-   [PTL 5] WO 2011/057706

Not only the dopant material but also a host material to be used isimportant for obtaining high luminous efficiency. A typical materialthat has been proposed as the host material is, for example,4,4′-bis(9-carbazolyl)biphenyl (hereinafter referred to as “CBP”) as acarbazole compound introduced in Patent Literature 2. When CBP is usedas a host material for a green phosphorescent light-emitting materialtypified by a tris(2-phenylpyridine)iridium complex (hereinafterreferred to as “Ir(ppy)3”), owing to the characteristic of CBP by whichthe flow of a hole is facilitated and the flow of an electron is madedifficult, a charge injection balance is broken and excessive holes flowout to an electron-transporting layer side. As a result, the efficiencyof light emission from Ir(ppy)3 reduces.

As described in the foregoing, a host material having a high tripletexcitation energy and balanced injecting/transporting characteristicsfor both charges (a hole and an electron) is needed for obtaining highluminous efficiency in an organic EL device. Further, a compound that iselectrochemically stable, and has high heat resistance and excellentamorphous stability has been desired, and hence an additionalimprovement has been required.

Patent Literature 3 discloses such a carbazole compound as shown belowas a host material for an organic EL device.

However, it is assumed that the carbazole derivative does not providesufficient luminous efficiency because the derivative has a phenyl groupat each of the 3- and 7-positions of dibenzofuran.

Patent Literature 4 discloses such a carbazole compound as shown belowas a host material for an organic EL device.

However, the disclosed compound is merely a compound obtained byintroducing carbazole to the 2-position of dibenzothiophene, and theliterature does not disclose the usefulness of an organic EL deviceusing the compound of the present invention obtained by introducingcarbazole to the 1-position of dibenzothiophene or dibenzofuran.

Patent Literature 4 discloses such a carbazole compound as shown belowas a host material for an organic EL device.

However, the disclosed compound is merely a compound obtained byintroducing carbazole to the 4-position of dibenzothiophene, and theliterature does not disclose the usefulness of an organic EL deviceusing a compound obtained by introducing carbazole to the 1-position ofdibenzothiophene or dibenzofuran.

Patent Literature 5 discloses such a carbazole compound as shown belowas a host material for an organic EL device.

The disclosed compound is characterized in that a nitrogen-containingsix-membered ring and carbazole are introduced, and the 3-position ofdibenzothiophene is substituted in the compound. However, the literaturedoes not disclose the usefulness of an organic EL device using acompound obtained by introducing carbazole to the 1-position ofdibenzothiophene or dibenzofuran.

SUMMARY OF INVENTION

In order to apply an organic EL device to a display device in a flatpanel display or the like, it is necessary to improve the luminousefficiency of the device and also to ensure sufficiently the stabilityin driving the device. The present invention has an object to provide,in view of the above-mentioned circumstances, an organic EL device,which has high efficiency, has high driving stability, and ispractically useful and a compound suitable for the organic EL device.

As a result of their extensive studies, the inventors of the presentinvention have found that the use of a compound, which has a carbazolegroup at the 1-position of dibenzothiophene or dibenzofuran and has aspecific substituent at any one of the 2- to 7-positions of thecarbazole group, in an organic EL device causes the device to showexcellent characteristics. Thus, the inventors have completed thepresent invention.

The present invention relates to an organic electroluminescent device,including: a substrate; an anode; an organic layer; and a cathode, theanode, the organic layer, and the cathode being laminated on thesubstrate, in which a carbazole compound represented by the generalformula (1) is used in at least one layer selected from the groupconsisting of a light-emitting layer, a hole-transporting layer, anelectron-transporting layer, a hole-blocking layer, and anelectron-blocking layer.

In the general formula (1), R¹ to R⁶ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 11 carbon atoms, or an aromatic group represented by thegeneral formula (2), and at least one of R¹ to R⁶ represents an aromaticgroup represented by the general formula (2), X's each independentlyrepresent CR⁹ or nitrogen, R⁷ to R⁹ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 11 carbon atoms, an aromatic hydrocarbon group having 6 to18 carbon atoms, or an aromatic heterocyclic group having 3 to 17 carbonatoms, and the aromatic hydrocarbon group and the aromatic heterocyclicgroup may each have a substituent, and E represents oxygen or sulfur.

In the general formula (1), at least one of R¹ to R⁶ represents amonovalent aromatic group represented by the general formula (2). It ispreferred that R² represent an aromatic group represented by the generalformula (2).

In addition, the carbazole compound represented by the general formula(1) is preferably a carbazole compound represented by the generalformula (3), more preferably a carbazole compound represented by thegeneral formula (4).

In the general formulae (1) to (4), the same symbols have the samemeanings. Therefore, the meanings of X, R⁷ to R⁹, and E are described inthe general formulae (1) and (2). It should be noted that in the generalformula (4), a plurality of R⁹'s may be identical to or different fromone another.

Although in the general formula (4), R⁷ to R⁹ are as described above, itis preferred that R⁷ to R⁹ each independently represent hydrogen, analkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to11 carbon atoms, an unsubstituted aromatic hydrocarbon group having 6 to18 carbon atoms, or an unsubstituted aromatic heterocyclic group having3 to 17 carbon atoms, and it is also preferred that R⁷ to R⁹ eachindependently represent a substituted aromatic hydrocarbon group orsubstituted aromatic heterocyclic group obtained by providing any sucharomatic hydrocarbon group or aromatic heterocyclic group with asubstituent. The substituent is preferably an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, an acyl group having 2 to 7 carbonatoms, an aromatic hydrocarbon group having 6 to 12 carbon atoms, or adiarylamino group having 12 to 24 carbon atoms. In addition, thearomatic heterocyclic group is preferably an unsubstituted aromaticheterocyclic group having 3 to 17 carbon atoms that is not anitrogen-containing six-membered ring, and the aromatic heterocyclicgroup can have a substituent. In the calculation of the number of carbonatoms, in the case of a substituted aromatic hydrocarbon group or asubstituted aromatic heterocyclic group, the number of carbon atoms of asubstituent is excluded. However, the number including the number ofcarbon atoms of the substituent preferably falls within the range.

In addition, the organic electroluminescent device of the presentinvention preferably includes a light-emitting layer containing thecarbazole compound represented by the general formula (1) and aphosphorescent light-emitting dopant.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view illustrating a structural example of anorganic EL device.

FIG. 2 shows a ¹H-NMR chart of a carbazole compound 8.

FIG. 3 shows a ¹H-NMR chart of a carbazole compound 49.

DESCRIPTION OF EMBODIMENTS

An organic electroluminescent device of the present invention contains acarbazole compound represented by the general formula (1) in a specificlayer. A carbazole compound represented by the general formula (3) or(4) is available as the carbazole compound represented by the generalformula (1). In the general formula (1), at least one of R¹ to R⁶represents an aromatic group represented by the general formula (2).

In the general formula (1), R¹ to R⁶ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 11 carbon atoms, or a monovalent aromatic group representedby the general formula (2), and at least one of R¹ to R⁶ represents anaromatic group represented by the general formula (2). R² preferablyrepresents an aromatic group represented by the general formula (2).

In the general formulae (2) and (3), X's each independently representCR⁹ or nitrogen. In addition, in the general formulae (2) to (4), R⁷ toR⁹ each independently represent hydrogen, an alkyl group having 1 to 10carbon atoms, a cycloalkyl group having 3 to 11 carbon atoms, anaromatic hydrocarbon group having 6 to 18 carbon atoms, or an aromaticheterocyclic group having 3 to 17 carbon atoms. Here, the aromatichydrocarbon group having 6 to 18 carbon atoms or the aromaticheterocyclic group having 3 to 17 carbon atoms can have a substituent.

When any one of R¹ to R⁹ represents an alkyl group having 1 to 10 carbonatoms or a cycloalkyl group having 3 to 11 carbon atoms, specificexamples thereof include a methyl group, an ethyl group, a propyl group,a butyl group, a hexyl group, a heptyl group, an octyl group, a nonylgroup, a decyl group, a cyclohexyl group, and a methylcyclohexyl group,and the group may be linear or branched. An alkyl group having 1 to 6carbon atoms or a cycloalkyl group having 3 to 8 carbon atoms ispreferred. Specific examples thereof include a methyl group, an ethylgroup, a propyl group, a butyl group, a pentyl group, a hexyl group, anda cyclohexyl group.

Next, the case where any one of R⁷ to R⁹ represents an aromatichydrocarbon group or an aromatic heterocyclic group is described.

The aromatic hydrocarbon group or the aromatic heterocyclic group is anaromatic hydrocarbon group having 6 to 18 carbon atoms or an aromaticheterocyclic group having 3 to 17 carbon atoms. Specific example thereofinclude monovalent groups obtained by removing one hydrogen atom from anaromatic compound selected from benzene, naphthalene, fluorene,anthracene, phenanthrene, fluoranthene, pyrene, chrysene, pyridine,pyrimidine, triazine, indole, quinoline, isoquinoline, quinoxaline,naphthyridine, carbazole, acridine, phenanthroline, phenazine,benzofuran, dibenzofuran, xanthene, oxanthrene, phenoxazine,benzothiophene, dibenzothiophene, thioxanthene, thianthrene,phenoxathiin, and phenothiazine. Of those, monovalent groups obtained byremoving one hydrogen atom from an aromatic compound selected from thefollowing compounds are preferred: benzene, indole, carbazole,benzofuran, dibenzofuran, benzothiophene, and dibenzothiophene.Monovalent groups obtained by removing one hydrogen atom from anaromatic compound selected from the following compounds are morepreferred: benzene and carbazole.

The aromatic hydrocarbon group or the aromatic heterocyclic group mayhave a substituent, and when any such group has a substituent, the totalnumber of substituents is 1 to 10, preferably 1 to 6, more preferably 1to 4. In addition, when the aromatic hydrocarbon group or the aromaticheterocyclic group has 2 or more substituents, the substituents may beidentical to or different from each other. In addition, in thecalculation of the number of carbon atoms of the aromatic hydrocarbongroup or the aromatic heterocyclic group, when any such group has asubstituent, the number of carbon atoms of the substituent is notincluded. When the calculation is performed while the number of carbonatoms of a substituent is included, in the case of an aromatichydrocarbon group, the number of carbon atoms falls within the range ofpreferably 6 to 50, more preferably 6 to 30. In the case of an aromaticheterocyclic group, the number of carbon atoms falls within the range ofpreferably 3 to 50, more preferably 5 to 30.

Preferred examples of the substituent include an alkyl group having 1 to6 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, analkoxy group having 1 to 6 carbon atoms, an acyl group having 2 to 7carbon atoms, an aromatic hydrocarbon group having 6 to 12 carbon atoms,and a diarylamino group having 12 to 24 carbon atoms. More preferredexamples thereof include an alkyl group having 1 to 4 carbon atoms, acycloalkyl group having 3 to 8 carbon atoms, an alkoxy group having 1 to4 carbon atoms, an acyl group having 2 to 5 carbon atoms, an aromatichydrocarbon group having 6 to 10 carbon atoms, and a diarylamino grouphaving 12 to 20 carbon atoms, and specific examples of such groups caninclude a methyl group, an ethyl group, a propyl group, a butyl group, acyclopentyl group, a cyclohexyl group, a methylcyclohexyl group, amethoxy group, an ethoxy group, a propoxy group, a butoxy group, ahexyloxy group, an acetyl group, a propionyl group, a phenyl group, atolyl group, a naphthyl group, a diphenylamino group, and adinaphthylamino group.

The compound represented by the general formula (1) is preferablyrepresented by the general formula (3) or (4). In each of the generalformulae (1), (3), and (4), E represents oxygen or sulfur. In each ofthe general formulae (3) and (4), R⁷ to R⁹ are as described above.

In the general formula (4), R⁷ to R⁹ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 11 carbon atoms, an aromatic hydrocarbon group having 6 to18 carbon atoms, or an aromatic heterocyclic group having 3 to 17 carbonatoms. However, in the case of the aromatic heterocyclic group having 3to 17 carbon atoms, it is not preferred that the group be anitrogen-containing six-membered ring.

Here, a substituted or unsubstituted aromatic heterocyclic group having3 to 17 carbon atoms that is not a nitrogen-containing six-membered ringis preferably a substituted or unsubstituted, fused aromaticheterocyclic group having 6 to 17 carbon atoms. Such aromaticheterocyclic group is the same as the aromatic heterocyclic groupdescribed above except that the group is not a nitrogen-containingsix-membered ring.

Specific examples of the compound represented by the general formula (1)are shown below. However, the compound is not limited to the exemplifiedcompounds.

When the carbazole compound represented by the general formula (1) isincorporated into at least one organic layer in an organic EL deviceformed by laminating an anode, a plurality of organic layers, and acathode on a substrate, an excellent organic electroluminescent deviceis provided. The organic layers preferably include at least alight-emitting layer, and preferably further include a hole-transportinglayer, an electron-transporting layer, a hole-blocking layer, or anelectron-blocking layer. A light-emitting layer, a hole-transportinglayer, an electron-transporting layer, a hole-blocking layer, or anelectron-blocking layer is suitable as the organic layer into which thecarbazole compound is incorporated. It is more preferred that thecarbazole compound be incorporated as a host material in alight-emitting layer containing a phosphorescent light-emitting dopant.

The organic EL device of the present invention includes organic layersincluding at least one light-emitting layer between an anode and acathode laminated on a substrate. In addition, at least one of theorganic layers contains the carbazole compound. The carbazole compoundrepresented by the general formula (1) is advantageously contained inthe light-emitting layer together with a phosphorescent light-emittingdopant.

Next, the structure of the organic EL device of the present invention isdescribed with reference to the drawings. However, the structure of theorganic EL device of the present invention is by no means limited to oneillustrated in the drawings.

FIG. 1 is a sectional view illustrating a structural example of ageneral organic EL device. Reference numerals 1, 2, 3, 4, 5, 6, and 7represent a substrate, an anode, a hole-injecting layer, ahole-transporting layer, a light-emitting layer, anelectron-transporting layer, and a cathode, respectively. The organic ELdevice of the present invention may include an exciton-blocking layeradjacent to the light-emitting layer, or may include anelectron-blocking layer between the light-emitting layer and thehole-injecting layer. The exciton-blocking layer may be inserted on anyof the anode side and the cathode side of the light-emitting layer, andmay also be inserted simultaneously on both sides. The organic EL deviceof the present invention includes the substrate, the anode, thelight-emitting layer, and the cathode as its essential layers. Theorganic EL device of the present invention preferably includes ahole-injecting/transporting layer and an electron-injecting/transportinglayer in addition to the essential layers, and more preferably includesa hole-blocking layer between the light-emitting layer and theelectron-injecting/transporting layer. It should be noted that thehole-injecting/transporting layer means any one or both of thehole-injecting layer and the hole-transporting layer, and that theelectron-injecting/transporting layer means any one or both of anelectron-injecting layer and the electron-transporting layer.

It should be noted that it is possible to adopt a reverse structure ascompared to FIG. 1, that is, a structure formed by laminating the layerson the substrate 1 in the order of the cathode 7, theelectron-transporting layer 6, the light-emitting layer 5, thehole-transporting layer 4, and the anode 2. In this case as well, alayer may be added or eliminated as required.

—Substrate—

The organic EL device of the present invention is preferably supportedby a substrate. The substrate is not particularly limited, and anysubstrate that has long been conventionally used for an organic ELdevice may be used. For example, a substrate made of glass, atransparent plastic, quartz, or the like may be used.

—Anode—

Preferably used as the anode in the organic EL device is an anode formedby using, as an electrode substance, any of a metal, an alloy, anelectrically conductive compound, and a mixture thereof, all of whichhave a large work function (4 eV or more). Specific examples of suchelectrode substance include metals such as Au and conductive transparentmaterials such as CuI, indium tin oxide (ITO), SnO₂, and ZnO. Further,it may be possible to use a material such as IDIXO (In₂O₃—ZnO), whichmay be used for manufacturing an amorphous, transparent conductive film.In order to produce the anode, it may be possible to form any of thoseelectrode substances into a thin film by using a method such as vapordeposition or sputtering and form a pattern having a desired shapethereon by photolithography. Alternatively, in the case of not requiringhigh pattern accuracy (about 100 μm or more), a pattern may be formedvia a mask having a desired shape when any of the above-mentionedelectrode substances is subjected to vapor deposition or sputtering.Alternatively, when a coatable substance such as an organic conductivecompound is used, it is also possible to use a wet film-forming methodsuch as a printing method or a coating method. When luminescence istaken out from the anode, the transmittance of the anode is desirablycontrolled to more than 10%. Further, the sheet resistance as the anodeis preferably several hundred Ω/□ or less. Further, the thickness of theresultant film is, depending on the material used, selected from usuallythe range of 10 to 1,000 nm, preferably the range of 10 to 200 nm.

—Cathode—

On the other hand, used as the cathode is a cathode formed by using, asan electrode substance, any of a metal (referred to aselectron-injecting metal), an alloy, an electrically conductivecompound, and a mixture thereof, all of which have a small work function(4 eV or less). Specific examples of such electrode substance includesodium, a sodium-potassium alloy, magnesium, lithium, a magnesium/coppermixture, a magnesium/silver mixture, a magnesium/aluminum mixture, amagnesium/indium mixture, an aluminum/aluminum oxide (Al₂O₃) mixture,indium, a lithium/aluminum mixture, and a rare earth metal. Of those,for example, a mixture of an electron-injecting metal and a second metalas a stable metal having a larger work function value than the formermetal, such as a magnesium/silver mixture, a magnesium/aluminum mixture,a magnesium/indium mixture, an aluminum/aluminum oxide (Al₂O₃) mixture,or a lithium/aluminum mixture, or aluminum is suitable from theviewpoints of electron-injecting property and durability againstoxidation or the like. The cathode may be produced by forming any ofthose electrode substances into a thin film by using a method such asvapor deposition or sputtering. Further, the sheet resistance as thecathode is preferably several hundred Ω/□ or less, and the thickness ofthe resultant film is selected from usually the range of 10 nm to 5 μm,preferably the range of 50 to 200 nm. It should be noted that, in orderfor luminescence produced to pass through, any one of the anode andcathode of the organic EL device is preferably transparent orsemi-transparent, because the light emission luminance improves.

Further, after any of the above-mentioned metals is formed into a filmhaving a thickness of 1 to 20 nm as a cathode, any of the conductivetransparent materials mentioned in the description of the anode isformed into a film on the cathode, thereby being able to produce atransparent or semi-transparent cathode. Then, by applying this, it ispossible to produce a device in which both the anode and cathode havetransparency.

—Light-Emitting Layer—

The light-emitting layer is a phosphorescent light-emitting layer, andcontains a phosphorescent light-emitting dopant and a host material. Itis recommended to use, as a material for the phosphorescentlight-emitting dopant, a material containing an organic metal complexincluding at least one metal selected from ruthenium, rhodium,palladium, silver, rhenium, osmium, iridium, platinum, and gold.Specific examples thereof include, but not limited to, the compoundsdisclosed in the following patent publications. The numbers of thepatent publications are shown below.

For example, WO 2009/073245 A1, WO 2009/046266 A1, WO 2007/095118 A3, WO2008/156879 A1, WO 2008/140657 A1, US 2008/261076 A, JP 2008-542203 A,WO 2008/054584 A1, JP 2008-505925 A, JP 2007-522126 A, JP 2004-506305 A,JP 2006-513278 A, JP 2006-50596 A, WO 2006/046980 A1, WO 2005/113704 A3,US 2005/260449 A, US 2005/2260448 A, US 2005/214576 A, WO 2005/076380A3, US 2005/119485 A, WO 2004/045001 A3, WO 2004/045000 A3, WO2006/100888 A1, WO 2007/004380 A1, WO 2007/023659 A1, WO 2008/035664 A1,JP 2003-272861 A, JP 2004-111193 A, JP 2004-319438 A, JP 2007-2080 A, JP2007-9009 A, JP 2007-227948 A, JP 2008-91906 A, JP 2008-311607 A, JP2009-19121 A, JP 2009-46601A, JP 2009-114369A, JP2003-253128A, JP2003-253129 A, JP 2003-253145 A, JP 2005-38847 A, JP 2005-82598 A, JP2005-139185 A, JP 2005-187473 A, JP 2005-220136 A, JP2006-63080A, JP2006-104201 A, JP2006-111623A, JP2006-213720A, JP2006-290891A,JP2006-298899 A, JP 2006-298900 A, WO 2007/018067 A1, WO 2007/058080 A1,WO 2007/058104 A1, JP 2006-131561 A, JP 2008-239565 A, JP 2008-266163 A,JP 2009-57367A, JP 2002-117978 A, JP 2003-123982 A, JP 2003-133074 A, JP2006-93542A, JP 2006-131524 A, JP 2006-261623 A, JP 2006-303383 A, JP2006-303394A, JP 2006-310479A, JP 2007-88105A, JP 2007-258550 A, JP2007-324309A, JP 2008-270737A, JP 2009-96800A, JP 2009-161524 A, WO2008/050733 A1, JP 2003-73387A, JP 2004-59433 A, JP 2004-155709 A, JP2006-104132 A, JP 2008-37848A, JP 2008-133212 A, JP 2009-57304 A, JP2009-286716A, JP 2010-83852 A, JP 2009-532546 A, JP 2009-536681 A, andJP 2009-542026 A.

Preferred examples of the phosphorescent light-emitting dopant includecomplexes such as Ir(ppy)3, complexes such as Ir(Bt)2•acac3, andcomplexes such as PtOEt3, the complexes each having a noble metalelement such as Ir as a central metal. Specific examples of thosecomplexes are shown below, but the complexes are not limited to thecompounds described below.

It is preferred that the content of the phosphorescent light-emittingdopant in the light-emitting layer fall within the range of 0.1 to 50 wt%, more preferably 1 to 30 wt %.

It is preferred to use, as a host material in the light-emitting layer,the carbazole compound represented by the general formula (1). However,when the carbazole compound is used in any of the organic layers otherthan the light-emitting layer, the material to be used in thelight-emitting layer may be any other host material other than thecarbazole compound, and the carbazole compound and any other hostmaterial may be used in combination. Further, a plurality of kinds ofknown host materials may be used in combination.

It is preferred to use, as a usable known host compound, a compound thathas a hole-transporting ability or an electron-transporting ability, iscapable of preventing luminescence from having a longer wavelength, andhas a high glass transition temperature.

Such other host materials are known because they are mentioned in manypatent literatures and the like, and hence may be chosen from those inthe patent literatures and the like. Specific examples of the hostmaterial include, but not particularly limited to, an indole derivative,a carbazole derivative, an indolocarbazole derivative, a triazolederivative, an oxazole derivative, an oxadiazole derivative, animidazole derivative, a polyarylalkane derivative, a pyrazolinederivative, a pyrazolone derivative, a phenylenediamine derivative, anarylamine derivative, an amino-substituted chalcone derivative, astyrylanthracene derivative, a fluorenone derivative, a hydrazonederivative, a stilbene derivative, a silazane derivative, an aromatictertiary amine compound, a styrylamine compound, an aromaticdimethylidene-based compound, a porphyrin-based compound, ananthraquinodimethane derivative, an anthrone derivative, adiphenylquinone derivative, a thiopyran dioxide derivative, aheterocyclic tetracarboxylic acid anhydride such as naphthaleneperylene, a phthalocyanine derivative, various metal complexes typifiedby a metal complex of an 8-quinolinol derivative, a metalphthalocyanine, and metal complexes of benzoxazole and benzothiazolederivatives, and polymer compounds such as a polysilane-based compound,a poly(N-vinylcarbazole) derivative, an aniline-based copolymer, athiophene oligomer, a polythiophene derivative, a polyphenylenederivative, a polyphenylenevinylene derivative, and a polyfluorenederivative.

—Injecting Layer—

The injecting layer refers to a layer formed between an electrode and anorganic layer for the purposes of lowering a driving voltage andimproving a light emission luminance, and includes a hole-injectinglayer and an electron-injecting layer. The injecting layer may beinterposed between the anode and the light-emitting layer or thehole-transporting layer, or may be interposed between the cathode andthe light-emitting layer or the electron-transporting layer. Theinjecting layer may be formed as required.

—Hole-Blocking Layer—

The hole-blocking layer has, in a broad sense, the function of anelectron-transporting layer, and is formed of a hole-blocking materialthat has a remarkably small ability to transport holes while having afunction of transporting electrons, and hence the hole-blocking layer iscapable of improving the probability of recombining an electron and ahole by blocking holes while transporting electrons.

The carbazole compound represented by the general formula (1) ispreferably used in the hole-blocking layer. However, when the carbazolecompound is used in any other organic layer, a known material for ahole-blocking layer may be used. In addition, it is possible to use, asa material for the hole-blocking layer, any of materials for theelectron-transporting layer to be described later as required.

—Electron-Blocking Layer—

The electron-blocking layer is formed of a material that has aremarkably small ability to transport electrons while having a functionof transporting holes, and hence the electron-blocking layer is capableof improving the probability of recombining an electron and a hole byblocking electrons while transporting holes.

Any of materials for the hole-transporting layer to be described latercan be used as required as a material for the electron-blocking layer.The thickness of the electron-blocking layer is preferably 3 to 100 nm,more preferably 5 to 30 nm.

—Exciton-Blocking Layer—

The exciton-blocking layer refers to a layer used for blocking excitonsproduced by the recombination of a hole and an electron in thelight-emitting layer from diffusing in charge-transporting layers. Theinsertion of this layer enables effective confinement of the excitons inthe light-emitting layer, thereby being able to improve the luminousefficiency of the device. The exciton-blocking layer may be inserted onany of the anode side and the cathode side of the adjacentlight-emitting layer, and may also be inserted simultaneously on bothsides.

As a material for the exciton-blocking layer, there are given, forexample, 1,3-dicarbazolylbenzene (mCP) andbis(2-methyl-8-quinolinolato)-4-phenylphenolatoaluminum(III) (BAlq).

—Hole-Transporting Layer—

The hole-transporting layer is formed of a hole-transporting materialhaving a function of transporting holes, and a single hole-transportinglayer or a plurality of hole-transporting layers may be formed.

The hole-transporting material has any one of hole-injecting property,hole-transporting property, and electron-blocking property, and any ofan organic compound and an inorganic compound may be used. It ispreferred to use the carbazole compound represented by the generalformula (1) in the hole-transporting layer. However, any compoundselected from conventionally known compounds may be used. Examples ofthe known hole-transporting material that may be used include a triazolederivative, an oxadiazole derivative, an imidazole derivative, apolyarylalkane derivative, a pyrazoline derivative and a pyrazolonederivative, a phenylenediamine derivative, an arylamine derivative, anamino-substituted chalcone derivative, an oxazole derivative, astyrylanthracene derivative, a fluorenone derivative, a hydrazonederivative, a stilbene derivative, a silazane derivative, ananiline-based copolymer, and a conductive high-molecular weightoligomer, in particular, a thiophene oligomer. However, a triazolederivative, an oxadiazole derivative, an imidazole derivative, anarylamine derivative, or an oxazole derivative is preferably used, andan arylamine derivative is more preferably used.

—Electron-Transporting Layer—

The electron-transporting layer is formed of a material having afunction of transporting electrons, and a single electron-transportinglayer or a plurality of electron-transporting layers may be formed.

An electron-transporting material (which also serves as a hole-blockingmaterial in some cases) has only to have a function of transferringelectrons injected from the cathode into the light-emitting layer.Although the carbazole compound represented by the general formula (1)according to the present invention is preferably used in theelectron-transporting layer, any compound selected from conventionallyknown compounds may be used. Examples thereof include anitro-substituted fluorene derivative, a diphenylquinone derivative, athiopyran dioxide derivative, a carbodiimide, a fluorenylidenemethanederivative, anthraquinodimethane and an anthrone derivative, and anoxadiazole derivative. Further, it is also possible to use, as theelectron-transporting material, a thiadiazole derivative prepared bysubstituting an oxygen atom on an oxadiazole ring with a sulfur atom inthe oxadiazole derivative and a quinoxaline derivative that has aquinoxaline ring known as an electron withdrawing group. Further, it isalso possible to use a polymer material in which any of those materialsis introduced in a polymer chain or is used as a polymer main chain.

EXAMPLES

Hereinafter, the present invention is described in more detail by way ofExamples. It should be appreciated that the present invention is notlimited to Examples below and may be carried out in various forms aslong as the various forms do not deviate from the gist of the presentinvention.

The routes described below were used to synthesize a carbazole compoundto be used as a material for a phosphorescent light-emitting device. Itshould be noted that the number of each compound corresponds to thenumber given to the exemplified compound.

Example 1 Synthesis of (Compound 8)

Under a nitrogen atmosphere, 18.84 g (0.124 mol) of2-methoxyphenylboronic acid, 24.00 g (0.124 mol) of1-bromo-2,6-difluorobenzene, 7.72 g (0.00496 mol) oftetrakis(triphenylphosphine)palladium(0), 600 ml of toluene, and 100 mlof ethanol were loaded, and then 200 ml of a 2 M aqueous solution ofsodium hydroxide were added to the mixture while the mixture was stirredat room temperature. The resultant was stirred at 90° C. for 5 hr, andwas then cooled to room temperature, followed by the washing of theorganic layer with distilled water (300 ml×3). After the organic layerhad been dried with anhydrous magnesium sulfate, magnesium sulfate wasseparated by filtration and then the solvent was distilled off underreduced pressure. The resultant residue was purified by silica gelcolumn chromatography to provide 10.01 g (0.0455 mol, 38% yield) of anintermediate (A1) as a white solid.

Under a nitrogen atmosphere, 10.00 g (0.0454 mol) of the intermediate(1) and 100 ml of dichloromethane were loaded, and then 20 ml of asolution of boron tribromide in dichloromethane were added to themixture while the mixture was stirred at 0° C. The resultant was stirredat room temperature for 6 hr, and then water was added thereto, followedby the washing of the organic layer with distilled water (30 ml×3).After the organic layer had been dried with anhydrous magnesium sulfate,magnesium sulfate was separated by filtration and then the solvent wasdistilled off under reduced pressure. The resultant residue was purifiedby silica gel column chromatography to provide 8.62 g (0.0418 mol, 92%yield) of an intermediate (A2) as a transparent liquid.

Under a nitrogen atmosphere, 8.62 g (0.0418 mol) of the intermediate(A2) and 230 ml of N-methyl-pyrrolidone were loaded, and then 11.56 g(0.0836 mol) of potassium carbonate were added to the mixture while themixture was stirred at room temperature. The resultant was stirred at180° C. for 3 hr, and was then cooled to room temperature, followed bythe separation of potassium carbonate by filtration. 900 ml of distilledwater were added to the filtrate and then the mixture was stirred atroom temperature. After that, the precipitated solid was separated byfiltration. The resultant solid was dissolved in dichloromethane andthen the organic layer was washed with distilled water (30 ml×3). Afterthe organic layer had been dried with anhydrous magnesium sulfate,magnesium sulfate was separated by filtration and then the solvent wasdistilled off under reduced pressure. The resultant residue was purifiedby silica gel column chromatography to provide 7.02 g (0.0377 mol, 90%yield) of an intermediate (A3) as a white solid.

Under a nitrogen atmosphere, 35 g (0.209 mol) of carbazole and 300 ml ofacetic acid were loaded, and then 24.24 g (0.146 mol) of potassiumiodide and 31.24 g (0.146 mol) of potassium iodate were added to themixture while the mixture was stirred at room temperature. The resultantwas stirred at 80° C. for 2 hr, and was then cooled to room temperature.300 ml of an aqueous solution of sodium hydrogen sulfite and 300 ml oftetrahydrofuran were added to the resultant, and then the mixture wasstirred at room temperature. 300 ml of toluene were added to theresultant and then the organic layer was washed with distilled water(200 ml×2). After the organic layer had been dried with anhydrousmagnesium sulfate, magnesium sulfate was separated by filtration andthen the solvent was distilled off under reduced pressure. The resultantresidue was purified by recrystallization to provide 20.75 g (0.0708mol) of an intermediate (A4) as a white solid.

Under a nitrogen atmosphere, 3.03 g (0.0752 mol) of sodium hydride and20 ml of dimethylformamide (DMF) were loaded, and then 20 ml of a DMFsolution in which 20.00 g (0.0682 mol) of the intermediate (A4) had beendissolved were added to the mixture while the mixture was stirred atroom temperature. The resultant was stirred at room temperature for 30min, and then 20 ml of a DMF solution in which 7.00 g (0.0376 mol) ofthe intermediate (A3) had been dissolved were added to the resultant.The mixture was stirred at 120° C. for 7 hr, and was then cooled to roomtemperature. 300 ml of distilled water were added to the mixture andthen the whole was stirred at room temperature. The precipitated solidwas separated by filtration. The resultant solid was dissolved intetrahydrofuran and then 200 ml of distilled water were added to thesolution. The mixture was extracted with toluene (100 ml×3) and then theorganic layer was dried with anhydrous magnesium sulfate. After that,magnesium sulfate was separated by filtration and then the solvent wasdistilled off under reduced pressure. The resultant residue was purifiedby silica gel column chromatography to provide 16.74 g (0.0364 mol, 97%yield) of an intermediate (A5) as a white solid.

Under a nitrogen atmosphere, 10.00 g (0.0218 mol) of the intermediate(A5), 8.13 g (0.0283 mol) of the intermediate (A6), 1.36 g (0.000872mol) of tetrakis(triphenylphosphine)palladium(0), 300 ml of toluene, and50 ml of ethanol were loaded, and then 40 ml of a 2 M aqueous solutionof sodium hydroxide were added to the mixture while the mixture wasstirred at room temperature. The resultant was stirred at 90° C. for 2hr, and was then cooled to room temperature, followed by the washing ofthe organic layer with distilled water (100 ml×2). After the organiclayer had been dried with anhydrous magnesium sulfate, magnesium sulfatewas separated by filtration and then the solvent was distilled off underreduced pressure. The resultant residue was purified by silica gelcolumn chromatography and recrystallization to provide 8.70 g (0.0151mol, 69% yield) of a (compound 8) as a white solid.

The APCI-TOFMS of the compound showed an [M+1] peak at an m/z of 575.FIG. 2 shows the results of its 1H-NMR measurement (measurement solvent:THF-d8).

Example 2

Under a nitrogen atmosphere, 9.00 g (0.0196 mol) of the intermediate(A5), 10.63 g (0.0235 mol) of the intermediate (A7), 1.22 g (0.000784mol) of tetrakis(triphenylphosphine)palladium(0), 300 ml of toluene, and50 ml of ethanol were loaded, and then 35 ml of a 2 M aqueous solutionof sodium hydroxide were added to the mixture while the mixture wasstirred at room temperature. The resultant was stirred at 70° C. for 7hr, and was then cooled to room temperature, followed by the washing ofthe organic layer with distilled water (100 ml×2). After the organiclayer had been dried with anhydrous magnesium sulfate, magnesium sulfatewas separated by filtration and then the solvent was distilled off underreduced pressure. The resultant residue was purified by silica gelcolumn chromatography and recrystallization to provide 1.61 g (0.00218mol, 9% yield) of a (compound 49) as a white solid.

The APCI-TOFMS of the compound showed an [M+1] peak at an m/z of 740.FIG. 3 shows the results of its 1H-NMR measurement (measurement solvent:THF-d8).

Example 3

Each thin film was laminated by a vacuum deposition method at a degreeof vacuum of 4.0×10⁻⁵ Pa on a glass substrate on which an anode formedof an ITO substrate having a thickness of 110 nm had been formed. First,CuPC was formed into a layer having a thickness of 20 nm on the ITO.Next, NPB was formed into a layer having a thickness of 20 nm to serveas a hole-transporting layer. Next, the (compound 8) as a host materialand Ir(ppy)₃ as a dopant were co-deposited from different depositionsources onto the hole-transporting layer to form a light-emitting layerhaving a thickness of 30 nm. At this time, the concentration of Ir(ppy)₃was 10 wt %. Next, Alq3 was formed into a layer having a thickness of 40nm to serve as an electron-transporting layer. Further, lithium fluoride(LiF) was formed into a layer having a thickness of 1 nm to serve as anelectron-injecting layer on the electron-transporting layer. Finally,aluminum (Al) was formed into a layer having a thickness of 70 nm toserve as an electrode on the electron-injecting layer. Thus, an organicEL device was produced.

An external power source was connected to the resultant organic ELdevice to apply a DC voltage to the device. As a result, it wasconfirmed that the device had such light-emitting characteristics asshown in Table 1.

Examples 4 to 11

Organic EL devices were each produced in the same manner as in Example 3except that compounds 1, 5, 6, 7, 24, 25, and 28 were synthesized in thesame manner as in Example 1 and the compound 1, 5, 6, 7, 24, 25, or 28,or the compound 49 obtained in Example 2 was used instead of thecompound 8 as the host material for the light-emitting layer in Example3.

Comparative Example 1

An organic EL device was produced in the same manner as in Example 3except that CEP was used as the host material for the light-emittinglayer in Example 3.

Comparative Example 2

An organic EL device was produced in the same manner as in Example 3except that a compound H-1 was used as the host material for thelight-emitting layer in Example 3.

It was found that the local maximum wavelength of the emission spectrumof each of the devices obtained in Examples 3 to 11, and ComparativeExamples 1 and 2 was 540 nm, and hence light emission from Ir(ppy)₃ wasobtained. Table 1 shows the respective light-emitting characteristics.The columns “luminance”, “voltage”, and “luminous efficiency” in Table 1show values (initial characteristics) at the time of driving at 20mA/cm².

TABLE 1 Visual luminous Luminance Voltage efficiency Host compound(cd/m²) (V) (lm/W) Example 3 8 2360 9.4 3.9 4 1 2120 9.3 3.6 5 5 21309.0 3.7 6 6 2170 9.3 3.7 7 7 2060 9.4 3.4 8 24 2560 8.9 4.5 9 25 22909.3 3.9 10  28 1985 9.1 3.4 11  49 2230 9.4 3.7 Comparative CBP 1120 8.72.0 Example 1 2 H-1 1320 9.3 2.2

Example 3 is improved in initial characteristics as compared toComparative Example 1 and Comparative Example 2. The foregoing showsthat the use of a compound, which has carbazole at the 1-position ofdibenzothiophene or dibenzofuran and has a specific substituent at anyone of the 2- to 7-positions of carbazole, in an organic EL deviceimproves the characteristics of the organic EL device. Thecharacteristics of the EL devices of Examples 4 to 11 are similarlygood, which also shows the superiority of the carbazole compoundrepresented by the general formula (1).

INDUSTRIAL APPLICABILITY

The carbazole compound represented by the general formula (1) to be usedin the organic electroluminescent device of the present invention mayenable the fine adjustment of hole and electron mobilities, and thecontrol of various energy values, i.e., an ionization potential (IP), anelectron affinity (EA), and a triplet energy (T1) because N of itscarbazole ring is bonded to the 1-position of dibenzothiophene ordibenzofuran and the compound has a specific substituent at any one ofthe 2- to 7-positions of the carbazole ring. In addition, it may bepossible to improve the stability of the carbazole compound in each ofactive states, i.e., oxidation, reduction, and excitation, and at thesame time, the compound has a good amorphous characteristic. As a resultof the foregoing, the compound can realize an organic EL device having along driving lifetime and high durability.

The organic EL device according to the present invention haslight-emitting characteristics, driving lifetime, and durability atpractically satisfactory levels. Thus, the organic EL device has a hightechnical value in applications to flat panel displays (display devicesfor portable phones, in-vehicle display devices, display devices for OAcomputers, televisions, and the like), light sources utilizingcharacteristics of planar light emitters (light sources in lightingequipment and copying machines and backlight sources in liquid crystaldisplays and instruments), sign boards, sign lamps, and the like.

The invention claimed is:
 1. An organic electroluminescent device,comprising: a substrate; an anode; an organic layer; and a cathode, theanode, the organic layer, and the cathode being laminated on thesubstrate, wherein the organic layer comprises at least one layerselected from the group consisting of a light-emitting layer, ahole-transporting layer, an electron-transporting layer, a hole-blockinglayer, and an electron-blocking layer, the at least one layer containinga carbazole compound represented by the general formula (1):

in the general formula (1), R¹ to R⁶ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 11 carbon atoms, or an aromatic group represented by thegeneral formula (2), and at least one of R¹ to R⁶ represents an aromaticgroup represented by the general formula (2), X's each independentlyrepresent CR⁹ or nitrogen, R⁷ to R⁹ each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 11 carbon atoms, an aromatic hydrocarbon group having 6 to18 carbon atoms, or an aromatic heterocyclic group having 3 to 17 carbonatoms, and the aromatic hydrocarbon group and the aromatic heterocyclicgroup may each have a substituent, and E represents oxygen or sulfur. 2.An organic electroluminescent device according to claim 1, wherein R² inthe general formula (1) represents an aromatic group represented by thegeneral formula (2).
 3. An organic electroluminescent device accordingto claim 1, wherein the carbazole compound comprises a carbazolecompound represented by the general formula (3):

in the general formula (3), X, R⁷, R⁸, and E are identical in meaning toX, R⁷, R⁸, and E in the general formulae (1) and (2).
 4. An organicelectroluminescent device according to claim 3, wherein the carbazolecompound comprises a carbazole compound represented by the generalformula (4):

in the general formula (4), R⁷, R⁸, and E are identical in meaning toR⁷, R⁸, and E in the general formula (3), and R⁹ is identical in meaningto R⁷ and a plurality of R⁹'s may be identical to or different from oneanother.
 5. An organic electroluminescent device according to claim 4,wherein R⁷ to R⁹ in the general formula (4) each independently representhydrogen, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl grouphaving 3 to 11 carbon atoms, an unsubstituted aromatic hydrocarbon grouphaving 6 to 18 carbon atoms, an unsubstituted aromatic heterocyclicgroup having 3 to 17 carbon atoms, or a substituted aromatic hydrocarbongroup or a substituted aromatic heterocyclic group obtained by providingthe unsubstituted aromatic hydrocarbon group or the unsubstitutedaromatic heterocyclic group with a substituent, and the substituentcomprises one kind selected from an alkyl group having 1 to 6 carbonatoms, a cycloalkyl group having 3 to 10 carbon atoms, an alkoxy grouphaving 1 to 6 carbon atoms, an acyl group having 2 to 7 carbon atoms, anaromatic hydrocarbon group having 6 to 12 carbon atoms, and adiarylamino group having 12 to 24 carbon atoms.
 6. An organicelectroluminescent device according to claim 1, wherein the layercontaining the carbazole compound comprises a light-emitting layercontaining a phosphorescent light-emitting dopant.
 7. An organicelectroluminescent device according to claim 3, wherein the layercontaining the carbazole compound comprises a light-emitting layercontaining a phosphorescent light-emitting dopant.